In an atomic power plant, decay heat is generated in a core even after a reactor stops, and steam is generated due to the heat. For example, in a boiling water-type reactor (hereinafter, will be referred to as BWR), in a case where an abnormal situation occurs in the reactor and the pressure in the reactor rises, the generated steam is partially caused to pass through a steam safety relief valve (hereinafter, will be referred to as SRV) and to be discharged to a pressure suppression pool (hereinafter, will be referred to as S/P) inside a wetwell (hereinafter, will be referred to as W/W) which is apart of a primary containment vessel (hereinafter, will be referred to as PCV), and the steam is condensed therein. In the BWR having such a mechanism, even a relatively small PCV can efficiently eliminate (condense) the steam generated due to the decay heat, and a rise of the pressure in the PCV is relaxed such that the pressure can be restrained from excessively rising.
In a general BWR, the SRV is installed on a main steam line inside a drywell (hereinafter, will be referred to as D/W) which is a part of the PCV. Piping (hereinafter, will be referred to as SRV exhaust pipe) leading from the SRV to the S/P passes through the D/W and passes through a W/W space (upper space of the S/P). Thereafter, the piping communicates with the inside of the S/P. Generally, a structural material which is called a quencher is connected to the terminal end of the SRV exhaust pipe and steam is dispersed and is discharged to the inside of the S/P such that the steam can be efficiently condensed inside the S/P. However, on the assumption of a case where a steam leakage from the SRV exhaust pipe occurs in the W/W space, there is a possibility that steam discharged from the SRV is not discharged to the inside of the S/P and the function of the S/P condensing steam is degraded. As a result thereof, there is a possibility that the rate of rise of the pressure in the PCV increases and countermeasures to increase the capacity of an instrument restraining the pressure of the PCV from rising are required.
In addition, in a case where steam leaks from the SRV exhaust pipe at a place other than the W/W space, for example, when a leakage occurs in the D/W, the leaked steam passes through a vent pipe and flows into the S/P, thereby being condensed. In addition, for example, when steam leaks below the water level of the S/P, the leaked steam is condensed due to S/P water around thereof. Therefore, even though the influence is small compared to a case where a leakage occurs in the W/W space, it is desirable that steam leakages at these places can also be excluded.
Normally, multiple systems of SRVs are installed. In consideration of a case where apart of the SRVs fails to be opened, a number of SRVs sufficient to restrain the pressure in a reactor from rising are installed.
In order to prevent the above-described steam leakage in the W/W space, a configuration having double SRV exhaust pipes in the W/W space has been proposed (refer to PTL 1). In addition, in order to restrain a local rise of the temperature of the S/P water caused due to steam which is released inside the S/P from the SRV, or in order to efficiently condense steam released inside the S/P, a configuration of controlling the SRV to be opened by using the temperature of the S/P water has been proposed (refer to PTL 2 and PTL 3). In addition, in order to retain the soundness of the PCV, a configuration of controlling opening of the SRV in a case where the temperature of the S/P water becomes equal to or higher than a certain temperature has been proposed (refer to PTL 4).